" node "

[trueblue]

What constitutes a "node" during load developement ?
I understand the desire to get the least velocity variance , but do not know what a node is, or what to look for .

 

[308 nate]

What constitutes a "node" during load developement ?
I understand the desire to get the least velocity variance , but do not know what a node is, or what to look for .

A node is a point along a standing wave where the wave has minimal amplitude. For instance, when tuning a load to a rifle barrel it is desired to find a load that produces the least vibration or at least consistent vibration. It can also work the other way,you can tune a barrel to a load by changing the length or by adding weight. I don't believe a node is neccessaril talking about E.S and velocity, but is also a key part in finding a node. For what good is finding a node if your next round is outside of that velocity node?

In short for the ultimate accuracy you want to find a load that produces the least amount of vibration as well as finding a load that produces the most consistent ignition and burn. There are many things that can change once you develop this load, such as temperature, humidity, of course changing powder and bullet lots. barrel fouling etc...etc... this is why when developing a load I like to find a powder/bullet/primer combination that has a fairly wide acceptable node/consistent combustion. I have had many people ask if their rifle will shoot the same point of impact with and without a muzzle brake and my answer is no as you are adding weight to the end of the barrel, there have also been cases when the existing load for the barrel shot worse by adding weight to the end of the barrel, as well as some that have shot better. Depending on the contour of the barrel the variance will be different.

Sometimes it can be very frustrating and sometimes you can land right on the money! I definitely don't have all the answers for getting there, but I do know it sure is a lot of fun when you do......

FWIW,
308Nate

 

[trueblue]

So, you look for the " widest acceptable node/cosistent combustion". What would be an indication of consistant combustion, consistant velocity readings on the chrono ? Also, how do you determine the width of the acceptable node , is that determined by the variance in powder charge that still yields low estreme spreads in velocity?

 

[308 nate]

So, you look for the " widest acceptable node/consistent combustion". What would be an indication of consistent combustion, consistent velocity Yes. readings on the chrono ? If you have one you trust. My preferred method is to shoot at 1K and watch my vertical spread Also, how do you determine the width of the acceptable node , is that determined by the variance in powder charge that still yields low extreme spreads in velocity? Right on! I like to have at least 100 FPS acceptable accuracy window

Again it's not a perfect world and sometimes this can be frustrating.

 

[trueblue]

Thanks, Nate.
I like the idea of shooting at distance and watching vertical spread.
For me chronographs can be unreliable sometimes.

 

[heikki02003]

Put a little more simply, a "node" is where your rifle, bullet, and powder charge produces a nice little group while developing a load. To explain this would require a huge discussion on barrel harmonics that I won't get into. Typically, us as reloaders are concerned with two "nodes". You'll find one somewhere in the bottom half of your min/max book values, and another one typically somewhere around max book value.
The problem is that with some powder, bullet, barrel combinations the "node" (remember small group) you find in your load development will be right in the middle of your min/max values, and going up to you max has not produced another "node". That means that your next node will be above max pressure. When this happens its time to change powder.
A very intelligent man by the name of Dan Newberry has come up with very good way of finding your optimal charge weight (OCW). I highly, highly recommend reading every word of his website and using his method.
Here is the link: Dan Newberry's OCW Load Development System

 

[royinidaho]

Interesting discussion.

Also interesting to slight personal modifications of the standard practice.

It seems that the idea is to get the smallest group with the widest variation of variables mainly velocity.

I have found for a couple of rifles that the same velocity with different powders produces very different results. Nodes are at different velocities and nodes are either more narrow or wider.

As Nate said: Again it's not a perfect world and sometimes this can be frustrating.

The fun thing is that once you get it, you have it and not much changes for quite a few rounds. Then is just load a few and harvest somethin' over and over again.

 

[Winchester 69]

It has to do with barrel vibrations. When the gun is fired, the barrel vibrates, and the tip of the barrel moves, influencing the direction of the bullet as it exits the barrel. When the barrel reaches the extent of its travel, it momentarily is motionless. Similarly, just before and after the node, the acceleration and deceleration are minimal. Theory has it that the bullets will group closely on target due to the minimized barrel tip movement. A good load will have your bullets exiting each time when the barrel is relatively motionless.

The term NOde means that NOthing is happening.
.

 

[royinidaho]

Go here, it'll scare ya....

Barrel Harmonics Mode Shape Movies